If you look at the sharpness of this lens for various cameras, you get:
I think that these results prove that there is something seriously wrong with the way you define sharpness. There is no way that D600/D3X and D800 are so close and D800E is so above.
For the D800/D800E comparison, I know that you compare the sharpness of the image without any sharpness applied to the picture. It is obvious that a camera with anti-aliasing filter needs (and can handle) more sharpening than a camera without one. Therefore, the comparison is not fair.
I stil don't understand why the D600 and D800 results are so close. It just does not match what you get when you compare a crop of a D800 and a crop of a D600 picture upscaled to 36MP.